If you are looking at running SQL Server in the cloud a key question you will ask is “Should I rent or Buy” SQL licenses. E.g. should you use the stock images and pay by the hour or should you buy your own licences.

Some facts that will help you decide:

SQL Server Enterprise Edition can vary in price from say 16,000 euro to 24,000 euro per four cores depending on your licensing scheme and bartering ability.

You MUST pay for software assurance at 20% per year to transfer licenses to the cloud (Azure or Amazon)

Azure charges about 1,164 euro per month for enterprise edition, per four cores.

Buying licences with SA gives you rights to use a “DR” instance without paying for its license. When renting you need to pay for DR while its turned on (not good for say a passive mirror).

So assuming full retail prices we can say the following:

If you are running for more than 2 years at 100% up time you should buy.

If you are powering down images then factor this in. So if 50% powered down, only buy if you are sweating the licences for > 4 years.

If you are running “warm” DR Servers then buy licenses if run for more than a year. Effectively buying licences becomes twice as appealing.

One thing I am looking at the moment is a scale out architecture where there may be two nodes up 100% of the time and then additional nodes scaled on demand. In this hybrid case it makes sense to buy licenses on the permanent nodes and “rent” on the elastic nodes.

Obviously this doesn’t take into account that renting gives you more flexibility, so is certainly the mode of choice for temporary environments.